1. Field of the Invention
The present invention relates generally to a method and apparatus for discriminating between datum as a function of an input from a specific even contributing the datum relative to a weighted average, or other threshold, of the data from a number of similar events. More specifically, the invention relates to a method and apparatus for continually updating the average, or other similar threshold, of a number of events, and selecting only those events which related to the threshold in a desired manner, i.e., deviated from the threshold a predetermined positive or negative amount.
2. Description of the Prior Art
The necessity of accepting or rejecting specific datum based upon the nature of a specific corresponding event providing such datum exists for a number of measurements. An example of such a requirement is the measurement of particles by means of scattered radiation as the particle passes through a beam of radiation. Since the beam edges are usually of less intensity than the center portions of such a beam, the data for particles passing through the edges of the beam are spurious in recording the particle as being of a smaller size as a result of less scattered radiation. However, since the particles will be moving at a substantially constant average velocity, particles passing through the edges of the beam induce scattering and a resulting signal for a shorter period than do particles passing through the beam proper. Accordingly, the validity of the datum is a fraction of the duration of the specific event. Thus, only datum exceeding a predetermined threshold would be considered valid. A similar requirement may exist for many other data-gathering operations. The problems and requirements will be considered with regard to duration with the understanding that parallel discussions exist for other parameters.
One rather common approach to the problem is to provide a fixed threshold duration below which the events are discounted. However, with a fixed threshold, experimental variations other than relative duration, i.e., a variation in the average particle velocity, will undesirably vary the percent of events which are accepted or rejected.
Mechanical means can also be utilized to preclude unacceptable data. For instance, with respect to the particle measurement apparatus, masks or conduits can be employed to guide the particles only through the center of the beam. The disadvantage of this approach lies in the fact that such masks or conduits themselves influence the flow of particles, particularly when the particles are of substantial size relative to the beam, and, thus, introduce an uncertainty into the results.